| Title | Pressure Interference Tests at the Wasabizawa Geothermal Field, Akita Prefecture, Japan |
|---|---|
| Authors | Hiroaki ASAI, Shigetaka NAKANISHI, Shigeo TEZUKA, Chitoshi AKASAKA, Kenji SASAKI, Kengo TAKIZAWA, Takashi KANEKO, Shuji AJIMA |
| Year | 2020 |
| Conference | World Geothermal Congress |
| Keywords | Wasabizawa, pressure transient test, pressure interference test, fractured reservoir, steam cap |
| Abstract | The Wasabizawa geothermal field is located in Akita prefecture, northeastern Honshu. Commercial operation of the Wasabizawa geothermal power station (46.199 MWe) began in 2019. The subsurface stratigraphy consists of a sequence of volcanic rocks overlying naturally-fractured granitic basement rocks. The geothermal reservoir is hosted by the naturally-fractured granitic rocks. Fault systems striking along NW-SE, NE-SW and E-W trends are inferred by geophysical surveys (gravity survey and MT & CSAMT surveys). Targeting these estimated fault zones, a total of 11 production and reinjection wells, in addition to five existing exploration wells which will be converted to production and injection wells, were drilled during construction of the power station, and an extensive heterogeneity of fracture distribution in the granitic basement rock was observed. To delineate the permeability structure for the area, numerous pressure transient tests were performed during short term production from and injection into newly drilled wells. Analyses of pressure interference data indicate that the reservoir has a modest transmissivity of 3-17 Darcy-m. Reservoir temperature and pressure profiles suggest that two phase regions (steam cap) may exist just below the cap rock in eastern part of the field where depth of reservoir top is relatively shallow. Relatively large value for the storage parameter ï¦ch (1-3 ï‚´ 10-7 m/Pa) obtained by pressure interference analysis in eastern production wellfield also suggests that steam cap exists at the top of the reservoir and affects the pressure transient response. |